SorCS2 dynamically interacts with TrkB and GluN2B to control neurotransmission and Huntington’s disease progression

Huntington9s disease (HD) is a fatal neurodegenerative disorder characterized by progressive motor dysfunction and loss of medium spiny neurons (MSNs) in dorsal striatum. Brain-derived neurotrophic factor (BDNF) sustains functionality and integrity of MSNs, and thus reduced BDNF signaling is integral to the disease. Here we show that SorCS2 is expressed in MSNs with reduced expression in R6/1 HD model, and that SorCS2 deficiency exacerbates the disease progression in R6/1 mice. Furthermore, we find that SorCS2 binds TrkB and the NMDA receptor subunit GluN2B, which is required to control neurotransmission in corticostriatal synapses. While BDNF stimulates SorCS2-TrkB complex formation to enable TrkB signaling, it disengages SorCS2 from GluN2B, leading to enrichment of the subunit at postsynaptic densities. Consequently, long-term potentiation (LTP) is abolished in SorCS2 deficient mice, despite increased striatal TrkB and unaltered BDNF expression. In contrast, the addition of exogenous BDNF rescues the phenotype. Finally, GluN2B, but not GluN2A, currents are also severely impaired in the SorCS2 KO mice. To conclude, we uncovered that SorCS2 dynamically targets TrkB and GluN2B to orchestrate BDNF-dependent plasticity in MSNs of dorsal striatum. We propose that SorCS2 deficiency impairs MSN function thereby increasing neuronal vulnerability and accelerating the motor deficits in Huntington9s disease.